Electromagnetic relays have been known in the electronics industry for many years. Such electromagnetic relays include the reed relay, which incorporates a reed switch. A reed switch is a magnetically activated device that typically includes two flat contact tongues that are merged in a hermetically sealed glass tube filled with a protective inert gas or vacuum. The switch is operated by an externally generated magnetic field, either from a coil or a permanent magnet. When the external magnetic field is enabled, the overlapping contact tongue ends attract each other and ultimately come into contact to close the switch. When the magnetic field is removed, the contact tongues demagnetize and spring back to return to their rest positions, thus opening the switch like member. A coil of wire is wrapped about the outside of the bobbin and connected to a source of electric current. The current flowing through the coil creates the desired magnetic field to actuate the reed switch contained within the bobbin housing. Some applications of reed devices require the switch to carry signals with frequencies in excess of 500 MHz. For these applications, a ground shield conductor, commonly made of copper, or brass or any suitably conductive metals is disposed about the body of the reed switch. The ground shield conductor is commonly in a cylindrical configuration. The shield conductor resides between the reed switch and the bobbin housing to form a co-axial high frequency transmission system. This co-axial system includes the outer shield conductor and the switch lead signal conductor co-axially through the center of the reed switch. The ground shield conductor is employed to contain the signal through the switch conductor in order to maintain the desired impedance of the signal path. For application at higher frequencies, a reed switch device must be ideally configured to match as closely as possible the desired impedance requirements of the circuit in which it is installed.
Within a circuit environment, a co-axial arrangement is preferred throughout the entire environment to maintain circuit integrity and the desired matched impedance. As stated above, the body of a reed switch includes the necessary coaxial environment. In addition, the signal trace on the user's circuit board commonly includes a “wave guide” where two ground leads reside on opposing sides of the signal lead and in the same plane or a “strip line” where a ground plane resides below the plane of the signal conductor. These techniques properly employed provide a two-dimensional co-axial-like environment, which is acceptable for maintaining the desired impedance for proper circuit function.
However, the reed switch device must be physically packaged and electrically interconnected to a circuit board carrying a given circuit configuration. It is common to terminate the shield and signal terminals to a lead frame architecture and enclose the entire assembly in a dielectric material like plastic for manufacturing and packaging ease. These leads may be formed in a gull-wing or “J” shape for surface mount capability. The signal leads or terminals exit out of the reed switch body and into the air in order to make the electrical interconnection to the circuit board. This transition of the signal leads from plastic dielectric to air creates an undesirable discontinuity of the protective co-axial environment found within the body of the switch itself. Such discontinuity creates inaccuracy and uncertainty in the impedance of the reed switch device. As a result, circuit designers must compensate for this problem by specifically designing their circuits to accommodate and anticipate the inherent problems associated with the discontinuity of the protective co-axial environment and the degradation of the rated impedance of the reed switch device. For example, the circuit may be tuned to compensate for the discontinuity by adding parasitic inductance and capacitance. This method of discontinuity compensation is not preferred because it complicates and slows the design process and can degrade the integrity of the circuit. There is a demand to reduce the need to tune the circuit as described above.
Generally, highly conductive materials are used to construct the signal leads in order to minimize impedance through the leads, thereby reducing the buildup of heat as well as preventing degradation of signal quality. However, the problem of inductance is not addressed by the composition of the leads. Inductance occurs when a magnetic field is created in response to the propagation of a current in one direction through a signal path, which sets up an opposing current in the signal path. Unwanted inductance in the signal path can degrade the high frequency capability of the circuit. This effect can be compensated for to a limited degree. As the frequency of the signal increases, inductance becomes an increasing problem, even with signal compensation. This property places practical constraint on the frequencies used, and thereby constrains the bandwidth of the device.
As consumer and industry demands for faster signal processing, increased bandwidth, and smaller component profiles increase, there exists a demand for small electronic devices that can operate into the microwave region of signal frequencies without a decrease in signal quality. More specifically, what is needed are compact devices that are capable of conducting very high frequency signals with little to no loss in signal quality.